The present invention has to do with wellhead equipment used in connection with a pumping oil well, preferably one pumped with a rotated rod string. For years, a typical conventional pumping wellhead for a rotary pumping oil well has been constructed as shown in FIG. 1. The assembly comprises from the bottom up: a flanged casing head attached to the well casing; a flanged tubing head having an internal hanger from which the well tubing string is suspended; a tubing head adapter having a flanged connection at its bottom end and a threaded connection of smaller diameter at its top end; a production blow-out preventer (B.O.P) body having top and bottom threaded connections and including side openings for receiving the B.O.P. ram components; a flow tee body having threaded bottom and top connections and a threaded or flanged side opening for connecting with a flow line; a polished rod stuffing box; and a rotary drive assembly for rotating the well""s rod string to power a downhole progressive cavity pump. These components, except for the rotary drive assembly, combine to form a vertical central bore extending therethrough. The polished rod of the rod string extends through this central bore.
The combination of the tubing head adapter, B.O.P. body and flow tee body components is commonly collectively referred to as a xe2x80x98pumping treexe2x80x99.
The assembly of wellhead components above the tubing head is usually referred to collectively as the xe2x80x98Christmas treexe2x80x99.
A recent improvement in the production wellhead art is disclosed in Canadian patent 2,197,584, issued Jul. 7, 1998 and re-issued May 16, 2000. This patent is owned by the present applicant. More particularly, this patent teaches integrating the tubing head adapter, B.O.P. body and flow tee body into a unitary structure, referred to as an xe2x80x98integral or composite pumping treexe2x80x99, by forging, casting or machining a single steel body. The composite pumping tree is illustrated in prior art FIGS. 2 and 2a and forms the lower end of the Christmas tree.
Another recent improvement in the production wellhead art is disclosed in Canadian patent application 2,280,581, filed by the present applicant. This patent application teaches integrating a tubing head adapter, shut-off valve body, B.O.P. body, and flow tee body into a composite pumping tree. This pumping tree is illustrated in prior art FIG. 3.
As previously stated, the rotary drive assembly usually has a stuffing box at its bottom end. The primary function of the stuffing box is to prevent upward leaking of fluid around the rotating polished rod. The stuffing box comprises a body or housing containing annular packing, which seals between the housing and the polished rod of the rod string.
Rotation of the polished rod eventually produces wear of the stuffing box packing. Therefore, changing the packing is part of the regular oilfield maintenance program.
Prior art FIGS. 1, 2 and 3 show a rotary drive assembly mounted to the stuffing box by an xe2x80x98openxe2x80x99 frame. The frame has side xe2x80x98windowsxe2x80x99 which enable access to the stuffing box packing gland, so as to change out the packing. However this frame introduces significant vertical separation between the rotary drive assembly and the pumping tree. This is undesirable as the rotary drive assembly vibrates when operating and applies offset forces that can create damage to the wellhead below. It is desirable to minimize the spacing between the rotary drive assembly and the pumping tree.
A modified rotary drive assembly is shown in FIG. 4. In this unit, the stuffing box housing is now integral with the rotary drive assembly. This variation has had the benefit of shortening the distance between the rotary drive assembly and the pumping tree.
However, it is more difficult to change out the packing of the stuffing box illustrated in FIG. 4. This process now requires:
shutting off the rotary drive assembly;
closing the production B.O.P by rotating the ram screws to advance the B.O.P rams into engagement with the polished rod;
providing a service rig having a line which is attached to the polished rod to suspend the rod string;
disconnecting the rod clamp normally suspending the rod string from and drivably connecting it with the rotary drive assembly;
disconnecting the rotary drive assembly from the pumping tree;
lifting the rotary drive assembly up using a second line from the service rig;
securing a rod clamp to the polished rod below the rotary drive assembly, to secure the rod string;
then fully removing the rotary drive assembly;
replacing the packing; and
re-assembling the equipment.
This process can also be dangerous. Since the rod string is driven and rotated, it has a built-in torque. This torque can generate a back-spin force, which can cause injury to personnel in various situations.
With this background in mind, it is an objective of the present invention to provide a polished rod locking assembly, forming part of the pumping tree and preferably being an integral component of the tree, which locking assembly can be actuated to clamp onto the polished rod to prevent back-spin and to grip the polished rod with sufficient force so as to suspend the weight of the rod string.
It is another objective to provide a leverage assembly in conjunction with the locking assembly, which is operative to apply high axial torque to the locking means to better secure the rod string.
It is another objective to provide a locking means capable of functioning like a blind ram to seal off the vertical bore of the wellhead, when the polished rod has parted in the stuffing box.
In accordance with one aspect of the invention, a polished rod locking assembly (xe2x80x9cPRL assemblyxe2x80x9d) is provided for inclusion as part of the pumping tree of a wellhead. This PRL assembly can be closed to clamp onto and frictionally engage the polished rod, to prevent back-spin, and to grip it with sufficient force so as to be able to suspend the rod string from the wellhead during stuffing box maintenance. These actions and results are hereafter collectively referred to as xe2x80x9csecuringxe2x80x9d the polished rod. More particularly, the PRL assembly comprises:
body means, which may be a separate component in a pumping tree formed of connected components or which preferably is integrated into a one piece integral pumping tree;
the body means forms a central bore (which forms part of the pumping tree vertical bore) and a pair of opposed, preferably horizontal, radial side openings. The side openings are internally threaded along part of their length and extend between the body means"" outer peripheral surface and the central bore;
an externally threaded locking member is positioned in each body side opening. These locking members can be radially advanced to frictionally engage the polished rod. Each locking member preferally comprises an inner cylindrical member and an outer, rotatable, threaded shaft. The shaft functions, when rotated or screwed, to advance or retract the inner member. The cylindrical member and shaft are interconnected so that the inner member does not rotate while the rotating shaft pushes or pulls it. The inner member has a vertically grooved inner end face which will embrace the polished rod as it contacts and frictionally engages it. More preferably, the inner member is formed in two parts. The innermost part is horizontally pivotally connected to the outer part and there is a slight clearance between the two parts. The outer part closely fits the internal surface of the side opening and remains stationary. The innermost part can tilt to a limited extent to accommodate misalignment of the polished rod. Each locking member seals against the surface forming the side opening in which it is contained. The outer end of the locking member protrudes from the body means;
the inner end of an external lever arm is connected, preferably at right angle, with the protruding outer end of one of the locking members, for rotation or turning thereof. Movement of the outer end of the arm will cause the locking member to turn to a limited extent about its axis. Threaded means, such as a swing bolt having an annular head, is pivotally connected by means, such as a bolt, with the outer end of the arm. A post is anchored to the body means or tree. The post supports a rotatable sleeve at its outer end. The swing bolt extends through the opening formed by the sleeve. A nut, threaded on the end of the swing bolt, can be turned with relatively low torque to induce a relatively powerful lineal pull by the swing bolt on the arm. This causes relatively high torque to be applied to the locking member which in turn applies high lineal, inwardly directed force on the polished rod.
As a consequence, the locking members can be activated by hand turning their outer ends, to bring their inner end faces into firm contact with the polished rod. The arm and swing bolt assembly can then be introduced and operated to bias the locking member with considerable lineal force against the polished rod to ensure sufficient frictional engagement to secure the heavy rod string.
The specific described assembly provides a lever arm for turning the locking member and a mechanical means for biasing the arm""s free end with a powerful lineal force to cause the locking member to secure the polished rod.
In another aspect, the PRL assembly is constructed so that it can operate as a xe2x80x9cblind ramxe2x80x9d to close the vertical bore of the pumping tree. More particularly, the body means and locking members are modified so that one locking member can retract sufficiently to enable the other locking member to extend across the vertical bore to close it. The other locking member carries seal means suitable for sealing the vertical bore from the radial openings when the locking member is in the closed position.